Seismic anisotropy of Precambrian lithosphere: Insights from Rayleigh wave tomography of the eastern Superior Craton

Abstract

The thick, seismically fast lithospheric keels underlying continental cores (cratons) are thought to have formed in the Precambrian and resisted subsequent tectonic destruction. A consensus is emerging from a variety of disciplines that keels are vertically stratified, but the processes that led to their development remain uncertain. Eastern Canada is a natural laboratory to study Precambrian lithospheric formation and evolution. It comprises the largest Archean craton in the world, the Superior Craton, surrounded by multiple Proterozoic orogenic belts. To investigate its lithospheric structure, we construct a frequency‐dependent anisotropic seismic model of the region using Rayleigh waves from teleseismic earthquakes recorded at broadband seismic stations across eastern Canada. The joint interpretation of phase velocity heterogeneity and azimuthal anisotropy patterns reveals a seismically fast and anisotropically complex Superior Craton. The upper lithosphere records fossilized Archean tectonic deformation: anisotropic patterns align with the orientation of the main tectonic boundaries at periods ≤110 s. This implies that cratonic blocks were strong enough to sustain plate‐scale deformation during collision at 2.5 Ga. Cratonic lithosphere with fossil anisotropy partially extends beneath adjacent Proterozoic belts. At periods sensitive to the lower lithosphere, we detect fast, more homogenous, and weakly anisotropic material, documenting postassembly lithospheric growth, possibly in a slow or stagnant convection regime. A heterogeneous, anisotropic transitional zone may also be present at the base of the keel. The detection of multiple lithospheric fabrics at different periods with distinct tectonic origins supports growing evidence that cratonization processes may be episodic and are not exclusively an Archean phenomenon.

Intraplate Volcanism and Regional Geodynamics in NE Asia Revealed by Anisotropic Rayleigh‐Wave Tomography

“…We repeat this procedure for each station pair and obtain a total of 1,643 phase velocity dispersion curves (Figure S2). All the measured dispersion curves are then inverted for 2‐D azimuthally anisotropic phase velocity maps at selected periods (Text S2, Deschamps et al, ; Lebedev & van der Hilst, ; Petrescu et al, ; Smith & Dahlen, ; Wang & Dahlen, ).…”

“…Broadband recordings of earthquake data are retrieved from 5 groups of seismic stations (Figure 2a The two-station method employed in this study to measure surface wave dispersion curves was first introduced by Sato (1955) and has been applied to numerous surface wave tomographic studies (e.g., Legendre et al, 2014Legendre et al, , 2016Petrescu et al, 2017). In this study, we implement the cross-correlation approach by Meier et al (2004) to obtain the Rayleigh-wave phase velocity dispersion curves.…”

Lateral Variations in Thermochemical Structure of the Eastern Canadian Shield

“…Here we take a step further and model the recent Rayleigh wave phase velocity model from Petrescu et al (2017) in terms of steady-state thermal profiles with a range of potential compositional structures for the mantle lithosphere. This will allow us to test (i) whether metasomatic alteration of the shallow mantle lithosphere is a general feature of Archean/Proterozoic shields as our previous study indicated, (ii) what mechanisms may be responsible for the average difference between Archean and Proterozoic structure within the study region, and (iii) how much lateral variation in thermal and compositional structure is required to explain the observed seismic structure.…”

“…To place constraints on the thermochemical structure of the lithospheric mantle in eastern Canada, we use the anisotropic Rayleigh wave phase velocity model of Petrescu et al (2017) (Figure 2). We sample the isotropic component of their velocity model at selected locations in the Superior and Grenville provinces (Figure 3), to obtain dispersion curves that describe how the phase velocity of fundamental Rayleigh waves varies with period.…”

Precambrian Plate Tectonics in Northern Hudson Bay: Evidence From P and S Wave Seismic Tomography and Analysis of Source Side Effects in Relative Arrival‐Time Data Sets

“…North America is thought to have grown episodically, with a chemically depleted upper ∼150–200 km underlain by younger, less depleted material. This change may be distinguished by a change in anisotropic fast direction (e.g., Darbyshire et al, ; Liddell et al, ; Petrescu et al, ). Sharp discontinuities imaged at midlithospheric depths by receiver function studies throughout cratonic North America (Abt et al, ) and within northern Hudson Bay have supported this episodic growth theory (e.g., Porritt et al, ; Rychert & Shearer, ).…”